A variety of abrasive articles are used to abrade or polish various substrates, including steel and other metals, woods, wood-like laminates, engineered boards, plastic, fiberglass, leather and ceramics. The abrasive articles are in any of a variety of forms, including sheets, discs, belts, wheels, and bands.
Many abrasive articles are used as discs in grinding assemblies. A typical abrasive sanding or grinding assembly includes: an annular back-up pad made from a resilient and reinforced material such as rubber or plastic and an abrasive disc having a backing plate and an abrasive surface (e.g., as provided by coated abrasive discs and non-woven abrasive discs) that includes abrasive material (e.g., abrasive grains and abrasive slurries). The abrasive disc and the back-up pad are typically mounted on a rotatable shaft of a tool and a retaining nut is used to secure the abrasive disc and back-up pad to the tool shaft. The shaft of the tool is inserted through holes in the center of the abrasive disc and back up pad. Frictional pressure is applied to the abrasive disc by screwing the nut onto the shaft to rotationally mount the disc to the back up pad by squeezing the abrasive disc against the back-up pad. In use, the shaft of the assembly is rotated and the abrasive surface of the disc is pressed against a substrate or workpiece with considerable force, to facilitate abrading of the substrate or workpiece. During the grinding process, the disc is subjected to severe stresses.
The abrasive material may completely cover or alternatively may only partially cover the surface of the backing plate. One particular style of abrasive disc uses an annular ring of abrasive material applied to the backing plate such that the inner radial boundary of the abrasive material is concentric with the backing plate. Examples of abrasive discs having an annulus of abrasive material include flap discs, non-woven surface conditioning discs, and grinding wheels.
The backing plates used in the abrasive articles (e.g., discs) are typically made of paper, certain polymeric materials such as phenolic impregnated fiberglass, cloth, nonwoven materials, vulcanized fiber, or combinations of these materials. Many of these materials, however, are not appropriate for certain applications because they are not of sufficient strength, flexibility, or impact resistance. Further, some of these materials age too rapidly. In some instances the materials are sensitive to liquids which are used as coolants and cutting fluids. As a result, a short useful product life can occur in certain applications.
One common backing plate material is vulcanized fiber. Vulcanized fiber backing plates are typically heat resistant and strong, which are advantageous characteristics when the coated abrasive is used in a grinding operation that imposes severe conditions of heat and pressure. For example, vulcanized fiber is used in certain grinding operations, such as weld grinding, contour grinding, and edge grinding, wherein the coated abrasive can be exposed to temperatures greater than 140° C. Vulcanized fiber backing plates, however are expensive, as well as hygroscopic, and thus sensitive to humidity.
Under extreme conditions of humidity (i.e., conditions of high and low humidity) vulcanized fiber typically either expands or shrinks, due, respectively, to water absorption or loss. As a result, an abrasive article made of vulcanized fiber tends to cup, causing a coated abrasive disc to curl either in a concave or a convex fashion. When this cupping or curling occurs, the affected abrasive disc does not lay flat against the back-up pad or support pad. This can effectively render the abrasive disc not useful.
To overcome the cupping and curling problems, other types of backing plate materials have been used, such as phenolic reinforced fiber backing plates. While these backing plates were typically more resistant to cupping or curling, the use of this type of material has led to other problems (e.g., cracking).
It is desirable to design abrasive discs to be quickly and easily removable from the rotatable shaft. One common technique for securing an abrasive disc to the shaft is typically accomplished by screwing a nut onto the rotary shaft of a tool, (thereby compressing the disc onto the back up pad). It is typically necessary to use tools (e.g., wrenches) to loosen and tighten the nut every time it is desirable to change the abrasive disc. The time required to change the abrasive disc can significantly limit the efficiency of the grinding task. To address this problem, other fasteners have been used. Unfortunately, such fasteners have not been conducive to quick and easy mounting and removal.
For example, a phenolic reinforced backing plate has been utilized in combination with an insert bonded or attached to a center hole formed through the back up pad. Another example is a metal grommet or nut that is adhesively bonded or mechanically attached to the backing plate. The manufacturing methods for making commercially useful embodiments utilizing either of these two types of mounting arrangements is relatively expensive. In part this expense can be attributed to the difficulty in drilling or punching holes or riveting the insert or grommet into backing plate without cracking the relatively brittle backing plate.
When relatively flexible backing plate materials are used, the backing plate tends to undesirably curl or otherwise become misshapen. Further, it can be more difficult to adequately secure the fastener to the backing plate.
There is a continuing need to develop manufacturing processes which provide an abrasive disc having adequate strength to withstand relatively harsh grinding environments which can be easily manufactured and mounted to and unmounted from a tool.